The present invention relates to semiconductor devices, and more particularly semiconductor devices in which torsional stresses are applied to channel regions thereof.
It is known that improved performance can be derived from a silicon device such as a field effect transistor when a stress of a sufficient magnitude and type is applied in a particular direction to the channel region of the device. A beneficial stress applied to the channel region of a field effect transistor (“FET”) can increase the amount of current that the FET conducts when it is turned on. Conversely, when a detrimental stress is applied to the channel region of a FET, the amount of current conducted by the FET decreases. Thus, for example, the performance of an n-type field effect transistor (“NFET”) provided in silicon can be improved when a relatively large tensile stress is applied to the device's channel region in a longitudinal direction, i.e., the direction of the length of the channel between the source and drain. On the other hand, the performance of a p-type field effect transistor (“PFET”) provided in silicon can be improved when a relatively large compressive stress is applied to the device's channel region in the longitudinal direction.
Various ways are known for applying stresses in the longitudinal direction to semiconductor devices. However, such ways can involve cumbersome processing and results can be difficult to control. Accordingly, more and better ways are sought for applying a stress to the channel region of a semiconductor device for altering the amount of current conducted by the device.